Electron mediator, sulfur role

In the transfer of reducing equivalents from the pyridine nucleotide pool, flavoproteins carry out a central role of mediating the conversion of the obligatory 2-electron reductant to 1-electron receptors such as hemes and iron-sulfur redox centers. In such a role, the semiquinone form of the flavin serves as a pivotal intermediate. The reduction of flavins and flavoproteins by reduced pyridine nucleotides has been extensively studied since the initial work of Singer and Kearney which showed that flavin reduction can occur in a non-enzyme catalyzed manner. The reduction proceeds as a 2-electron process since the formation of a nicotinamide semiquinone (a necessary intermediate in a 1-electron process) has been... 

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